1. Field of the Invention
The present invention relates to an apparatus for manufacturing a semiconductor device. More particularly, the present invention relates to a shower head provided to supply a reactant gas using plasma to a reaction chamber in a wafer treatment apparatus.
2. Description of the Related Art
As the integration density of semiconductor devices increases, a design rule decreases and the diameter of a wafer increases. Large wafers often undergo multiple steps for fabricating semiconductor devices, including, for example, deposition processes for depositing material layers on a wafer or etch processes for etching material layers on the wafer in a predetermined pattern by supplying a reactant gas from the upper portion of a reaction chamber for depositing or etching the wafer. In particular, as wafer sizes increase, during etch processes, it is important to optimize uniformity in etch rates over the entire wafer surface.
In a typical etching apparatus, a reactant gas, which is required for etching, is introduced into a reaction chamber by a downstream method whereby the gas is supplied from an upper electrode and pumped out into the periphery of a lower electrode. In order to evenly distribute the reactant gas within the reaction chamber, a shower head including several baffles, each of which has a plurality of through holes, is installed at the upper part of the reaction chamber. In a conventional shower head, the respective positions of the through holes and a gap between the baffles are fixed.
The function of the baffles provided in the shower head is to control the distribution of a flow of gas within an upper electrode, i.e., a gas distribution plate (GDP), of the etching apparatus. Typically, a gas distribution function of the baffle is determined by the gap between the baffles and an opening ratio of the through holes formed in each of the baffles. However, since the respective positions of the through holes provided in each baffle and the gap between the baffles are fixed in the conventional shower head, distribution in etch rates varies over the entire wafer surface each time a process to be performed in an etching apparatus is changed. Thus, the configuration of the conventional shower head involves limitations in developing a new process. Furthermore, development of a new etching apparatus usually requires numerous simulation processes and significant expense.
For example, in the case of an etch process for forming a gate electrode on a wafer, it may not be desirable to obtain etching uniformity over the entire wafer surface during an etch process step for forming an etch mask layer before gate patterning. Furthermore, if an etch process including multiple steps is performed, uniformity in etch rate on the wafer varies from one step to another. However, in the conventional shower head in which the respective positions of the through holes provided in each baffle and the gap between the baffles are fixed, it is impossible to supply different amounts of gas to different positions on the wafer, thereby increasing the difficulty to optimize the uniformity of a pattern to be formed over the entire wafer surface. Problems associated with an unevenness in an etch rate during an etch process during a fabrication process for a semiconductor device adversely affect the performance of the device and yields.